1. Technical Field
This invention relates to precast retaining wall modules and specifically to modules having a face panel and a rearwardly extending retaining stem. The invention also relates to retaining walls assembled with such modules.
2. Background Art
U.S. Pat. No. 4,684,294 of O'Neill discloses a precast concrete retaining wall construction element having a rectangular face panel and an integral embedment beam. The embedment beam extends perpendicularly from the center of the rear surface of the face panel, so that the element is T-shaped in plan view.
The embedment beam has indentations in its side surfaces to increase frictional engagement with earth backfill, and a sloping rear edge of the embedment beam is provided with a V-shaped groove or a sawtooth profile for the same purpose. A front lip on the upper edge of a face panel of one element engages a corresponding notch in the lower edge of the face panel of an element stacked on top, to key the two elements together.
The elements of U.S. Pat. No. 4,684,294 can be assembled in adjacent vertical "stack bonded" columns with the embedment beam of each course resting on the embedment beam of the element below. A drawback to this arrangement is that there is no interengagement between the elements of adjacent columns. The elements also can be assembled in a staggered "brick bonded" array, but this requires separate shear key beams extending across the embedment beams of each course for the embedment beams of the staggered elements of the next course to rest on.
Although the indentations and other means for increasing frictional engagement with the earth backfill increase the resistance of an assembly of these elements to overturning forces exerted by the backfill, this increased resistance is small compared with that obtainable from the total mass of earth backfilled between the embedment beams.
Another arrangement for anchoring face elements of a retaining wall are disclosed in U.S. Pat. Nos. 4,343,572 and No. 4,616,959 of Hilfiker. In the '572 patent a rigid face member is held in place by vertically spaced anchor elements in the form of horizontal wire grids embedded in earth backfill behind the face member. The '959 patent substitutes noncorrodible polymer mats for the wire grids and secures the mats between courses of stacked preformed concrete panels. The restraining force exerted by the mats on the wall members depends on the frictional force developed between the mats and the surrounding earth.
In U.S. Pat. No. 4,592,678 of McNinch, Jr. et al. overturning resistance is supplied to a stacked array of double-T elements by vertical tension rods extending upward from a massive concrete footing through holes near the rear ends of the double stems of the elements. Nuts at threaded upper ends of the tension rods secure the stems to the footing. By having a stem located one quarter of the distance from each end, the face panels of McNinch, Jr. et al. can be stacked in "brick bonded" staggered courses with both stems of each double-T element resting on stems of elements in the course below. Other than through the relatively low frictional force between their smooth faces and the surrounding backfill, however, the double stems of these elements do not take advantage of the mass of the backfill material to resist the overturning force exerted of the backfill.